1. Field of the Invention
The present invention relates to a drive transmitting device and an image forming apparatus using the same.
2. Description of the Related Art
In an image forming apparatus such as copiers, facsimiles, and printers, it has been common that an image is formed and carried by the surface movement of endless moving members such as rollers and endless belts. For example, in an electrophotographic image forming apparatus, endless surface movement of a latent image carrying member in a form of a rotating drum is used to form a latent image based on light scanning, develop it, and carry a visible image obtained by developing to a transfer position. Endless surface movement of a developing roller that rotates is used to carry a developer to a visible image on a latent image carrying member. Additionally, endless surface movement of an endless intermediate transfer belt is used to carry its surface to a transfer position corresponding to a photoconductor and to transfer a visible image on the photoconductor to a surface of the belt.
The image forming apparatus having such a configuration may produce adverse effects on an image due to variation of surface velocity (hereinafter, “velocity variation”) in an endless moving member. A tandem system of image forming apparatus disclosed in Japanese Patent Application Laid-open No. H15-57855 particularly causes color displacements due to velocity variation of a latent image carrying member. A tandem system is a system that visible images of different colors that are each formed on a plurality of latent image carrying members are overlapped and transferred onto a transfer member to form a multicolor image. The latent image carrying members generate velocity variation on an individual circle basis respectively so that the visible images of each color are transferred with their positions deviated one another, causing color deviation.
Velocity variation in an endless moving member is caused by various factors. For example, a configuration of transmitting a driving force from a driving motor to an endless moving member through a plurality of gears causes velocity variation of an endless moving member due to overlap of velocity variation of rotating gears based on decentering of an individual gear and a difference in mating gears. On the contrary, in a configuration of arranging an endless moving member and a driving motor on a straight line and each other's rotating shaft end surfaces are faced each other to couple a rotation driving force through coupling at each other's opposed positions, velocity variation of an endless moving member due to decentering of a gear or a difference in mating gears does not occur. Instead, in a relation that a driving shaft of a driving motor and a rotation shaft of an endless moving member are skew due to an imposed difference, velocity variation of an endless moving member may occur.
On the other hand, a constant velocity joint as disclosed in Japanese Published Examined Patent Application No. S52-34699 has been widely known as one of drive transmitting mechanisms that transmit a rotation driving force from a driving source to a driven member such as a vehicle shaft. The constant velocity joint is used to couple a rotation driving force between a driving source (a motor or an engine) and a driven member that are arranged each other on a straight line
in the same manner as through coupling, allowing an angle of deviation between a driving shaft and a driven member and enabling transmitting a rotation driving force between both of them at constant velocity.
However, because a constant velocity joint is originally used to transmit rotation velocity on a driving side directly to a driven side, when the driving side rotates with velocity variation, the variation is directly transmitted to the driven side. Therefore, it is necessary to rotate a driving-side rotating member of a constant velocity joint without velocity variation to drive a driven member without velocity variation. When a driving-side rotating member of a constant velocity joint and a driving shaft of a driving motor are connected under shaft misalignment due to an imposed difference, however, even if the driving shaft of the driving motor rotates without velocity variation, the driving-side rotating member of the constant velocity joint rotates with velocity variation. As a result, this causes velocity variation of a driven member such as a latent image carrying member.